The present invention is related to the modifying of substrates such as monofilaments, bundles of monofilaments fibrous structural materials, fibrous high-strength materials, fibrous construction materials, and fibrous engineered materials with a modifying agent comprised of, or conveyed by a supercritical or near-critical fluid.
Methods have been developed for the coating or modification of monofilaments, bundles of monofilamnents, fibrous structural materials, fibrous high-strength materials, fibrous construction materials, and fibrous engineered materials, including optical fibers, filaments, cables, fiberglass, glass fibers, ceramic fibers, graphite fibers, composites fibers, metal fibers and wires, that may be constructed of metals, alloys, inorganics, organometallics, salts, minerals, structural polymers, single-strand polymers, filamentous polymers, and the like. For example, polystyrene is known to be a good coating for glass optical fibers to increase durability. These coatings, however, are generally applied in a variety of ways with chemical treatment processes. Some of these methods of chemical treatment (for coating, impregnation, surface modification, etc.) include solvent-based systems and melt-based systems.
Solvent-based chemical treatment systems can include organic or inorganic materials in solutions such as aqueous solutions wherein the organic or inorganic material is dissolved, suspended, or otherwise dispersed in the solution. In the area of coating of glass fibers, U.S. Pat. Nos. 5,055,119, 5,034,276 and 3,473,950 disclose examples of such chemical treatments. Typically, with chemical treatment of some of the prior art, solvents are used to lower the viscosity of the chemical treatment to facilitate wetting of the glass fibers. The solvent is substantially unreactive with the other constituents of the chemical treatment and is driven out of the chemical treatment after the wetting of the glass fibers. In each process for applying solvent-based chemical treatments, an external source such as heat can be used to evaporate or otherwise remove the water or other solvent from the applied chemical treatment, leaving a coating of organic material on the glass fibers. With melt-based chemical treatment systems, thermoplastic-type organic solids can be melted and applied to various fibrous structures. Again, in the area of glass coating, U.S. Pat. Nos. 4,567,102, 4,537,610, 3,783,001 and 3,473,950 disclose examples of such melt-based chemical treatments of glass fibers. These methods and others have been used in the prior art to coat various elongated materials including monofilaments, bundles of monofilaments, and fibrous structures.
Supercritical fluids have been used previously to coat elongated materials such as fibers, metals, and the like. However, when such supercritical fluids have been used, they have typically been applied by one of a few methods. Several of these techniques involve the application of one or more modifying agent by batch soaking in an enclosed chamber. Other methods include processes based upon spraying from a pressurized chamber through a narrow nozzle.
With regard to spray-on deposition, air pressure sprayers have been used to contain supercritical and near-critical fluids (carriers) containing coating material. Upon spraying of the fluid onto the substrate, the supercritical fluid carrying the coating material leaves the high pressure environment and is exposed to a normal atmospheric environment. Thus, the supercritical fluid is exposed to low pressure and can evaporates leaving behind a coating material or modifying agent. This coating material or modifying agent can be deposited onto, or modify the substrate. Examples of typical spray depositions of the prior art include U.S. Pat. Nos. 4,582,731, 4,734,227, 4,734,451, 4,970,093, 5,032,568, 5,213,851, and 5,997,956. Regarding supercritical fluid batch processes, the substrate is typically immersed and then the pressure is dropped, depositing the coating. This is usually followed by a drying stage. In a related embodiment, fluorocarbon dipolymers can be used to enhance solubility of polar components in supercritical fluid. However, this is still a batch process.
Though the use of liquified gas, supercritical fluids, and near-critical liquids and gases have been used to coat solid or other fibrous substrates in the prior art, none presently known by the applicant appear to provide a system and method for modifying substrates such as monofilaments, bundles of monofilaments, fibrous structural materials in a continuous system that does not utilize spray-on or batch coating processes.
It has not been recognized that providing methods of coating monofilaments, bundles of monofilaments, and fibrous structural materials in a continuous system would be a significant advance in the art. Thus, it would be useful to provide methods of physically or chemically modifying such substrates in accordance with the principles disclosed herein.
The present invention is drawn to a method of modifying elongated monofilaments and bundles of monofilament, preferably utilizing any device related to that described in accompanying FIG. 1. The basic method can be broken down into several steps. One of the steps includes providing a treatment apparatus chamber having a passageway passing entirely therethrough, wherein the passageway comprises a first region, a second region, and a constricted medial region between the first region and the second region. An additional step involves passing a monofilament or a bundle of monofilaments through the passageway so that the monofilament or bundle of monofilaments move continuously therethrough. As the monofilament or bundle of monofilaments is passed through the passageway, the step of introducing a chemical treatment mixture into the constricted medial region of the passageway is carried out. The chemical treatment mixture comprises a modifying composition in a carrier medium that can be a supercritical fluid, a near-critical fluid, a superheated fluid, a superheated liquid, or a liquified gas. Thus, the modifying composition can be separated from the carrier medium upon a pressure drop when the mixture is flowed through the constricted region of the passageway. Preferably, the pressure drop causes a rapid expansion of the carrier medium, though this is not required. Once the substrate has been modified, optionally, the carrier medium and any unused modifying composition can be removed and/or recycled for further use. This method can also be carried out using different substrates than monofilaments and bundles of monofilaments. For example, a similar method can be carried out by applying a modifying composition to a fibrous structural material, such as roving material, according to the steps described above.